1. Technical Field
The present invention generally relates to a semiconductor device and a method of manufacturing the same, more specifically, to a semiconductor device including a cell string of a three-dimensional structure, and a method of manufacturing the same.
2. Related Art
Generally, a cell string of a semiconductor device is formed to be a two-dimensional structure in which memory cells are formed to be a single layer on a substrate. In this way, integration of the two-dimensional cell string can be increased by using a fine pattern forming technology and reducing a flat area occupied by the memory cells.
As the above-described technology for increasing the integration of the two-dimensional cell string has come to a limit, a three-dimensional cell string in which memory cells are stacked on a substrate in multiple layers has been proposed. Integration of the three-dimensional cell string can be increased without reducing a flat area occupied by the memory cells.
The three-dimensional cell string includes memory cells connected in series and disposed in various structures. For example, the three-dimensional cell string may include a cell string by connecting the memory cells stacked in two rows with a pipe transistor. In this case, due to limitations in a conventional manufacturing process, a gate material of the pipe transistor has its limits. More specifically, a gate of the pipe transistor is formed of silicon. Accordingly, it is difficult to obtain a stable operation characteristic of the pipe transistor thereby degrading reliability of the semiconductor device.